1. Field of the Invention
The present invention relates to a film-forming substance for temporarily opacifying transparent or translucent surfaces made of glass or rigid or flexible plastic (film), for example, in order to protect greenhouses from insolation.
2. Discussion of Background Information
According to a particularly interesting, although non-limiting application, the present invention addresses a problem currently encountered by farmers and horticulturists who must protect their greenhouse crops from the insolation effects.
The problem is to find an opacifying, rain-resistant substance that can be eliminated easily and quickly at the end of an extremely sunny season, or during a hot, temporarily sunless season, if necessary.
The products that are currently used do not make it possible to solve this problem in a satisfactory manner, but only partially by applying either irritating acid based liquids, which are very harmful to the environment, the greenhouses armatures, and the films made of plastic or, exceptionally, liquids based on alkaline agents whose cleaning efficiency on the associated paint is markedly inadequate and not immediate.
Practically, it is always necessary to brush the greenhouse glazings to obtain a good result, which farmers do not appreciate at all, in view of the waste of time and the danger posed by roofs difficult to access.
U.S. Pat. No. 4,626,559 proposes a non-permanent ornamental paint adapted to be applied on vehicles to indicate xe2x80x9ctheir sponsors,xe2x80x9d for example, in a race, and which has the advantage of not damaging the outer coating of the vehicles. This non-permanent ornamental paint includes an acid acrylic resin in aqueous dispersion and the non-permanent paint can be removed with water by rubbing.
Furthermore, the removal of traditional screen substances based on aqueous dispersion of styrene acrylic ester copolymers or acrylate copolymers is impossible with alkaline medium.
The present invention relates to a film-forming aqueous composition for temporarily opacifying at least one transparent or translucent surface of a greenhouse, the surface being made of a material selected from glass, rigid plastic or flexible plastic, the aqueous composition comprising: an alkaline agent; at least two binders constituted by at least two resins based on acrylic derivatives, each having an acid index greater than 60, wherein at least one of the at least two binders is in solid form and the other is in aqueous dispersion; and at least one filler or pigment.
The at least one filler can be selected from calcium carbonate, silica, silicate, barium sulphate, titanium oxide, or zinc oxide. Preferably, the at least one filler is calcium carbonate and the calcium carbonate has a particle size of 1 xcexcm.
The at least one pigment can be selected from mineral or organic colored pigment.
The at least one binder in dry form can be present in an amount from 0.5 to 3 weight percent of the total weight of the composition. Preferably, the at least one binder in dry form comprises methyl methacrylate.
The film-forming composition can also include at least one of cellulose ether thickening agent, dispersing agent, antifoaming agent or bactericide.
In a preferred aspect of the present invention, the cellulose ether thickening agent can be present in an amount of 0.1 to 0.5 weight percent of the total weight of the composition. The at least one dispersing agent can be selected from ammonium polyacrylate or potassium polycarboxylate and can be present in an amount of 0.1 to 2 weight percent of the total weight of the composition. The anti-foaming agent can be present in an amount of 0.1 to 0.4 weight percent of the total weight of the composition. The bactericide can be present in an amount of 0.1 to 0.3 weight percent of the total weight of the composition; and finely ground calcium carbonate and organic pigment can be present in an amount from 40 to 60 weight percent of the total weight of the composition, the remainder being water; and wherein the at least one binder in dry form can be present in an amount from 0.5 to 3 weight percent and wherein the alkaline agent is 25% strength ammonia and can be present in an amount from 0.2 to 0.6 weight percent of the total weight of the composition.
The present invention also relates to a method for temporarily opacifying at least one transparent or translucent surface of a greenhouse, the surface being made of a material selected from glass, rigid plastic or flexible plastic, comprising: applying to the at least one transparent or translucent surface an aqueous film-forming aqueous composition comprising a first alkaline agent, at least two binders constituted by at least two resins based on acrylic derivatives, each having an acid index greater than 60, wherein at least one of the at least two binders is in solid form and the other is in aqueous dispersion; and at least one filler or pigment, thereby forming an opacifying film on the at least one transparent or translucent surface, the opacifying film being capable of removal.
The at least one filler can be selected from calcium carbonate, silica, silicate, barium sulphate, titanium oxide, or zinc oxide. Preferably, the at least one filler is calcium carbonate and has a particle size of 1 xcexcm.
The at least one pigment can be selected from mineral or organic colored pigment.
In another aspect of the present invention, the method for temporarily opacifying at least one transparent or translucent surface of a greenhouse provides for removing the opacifying film with an aqueous cleaning solution comprising a second alkaline agent selected from sodium hydroxide, sodium carbonate, sodium salt of ethylene diamine tetraacetic acid or mixtures thereof or alternatively for removing the opacifying film with an acid aqueous cleaning solution.
In a preferred aspect of the present invention, the opacifying film can be removed by spraying the aqueous cleaning solution.
In another aspect of the present invention, the cleaning solution can contain the second alkaline agent in an amount from 0.2 to 3 weight percent of the total weight of the aqueous cleaning solution.
In yet another aspect of the present invention, the at least one binder in dry form can be present in an amount from 0.5 to 3 weight percent of the total weight of the composition and preferably comprises methyl methacrylate.
The film-forming composition can further comprise at least one of cellulose ether thickening agent, dispersing agent, antifoaming agent or bactericide.
In another preferred aspect of the present invention, the film-forming composition can further comprise cellulose ether thickening agent in an amount of 0.1 to 0.5 weight percent of the total weight of the composition, at least one dispersing agent selected from ammonium polyacrylate or potassium polycarboxylate in an amount of 0.1 to 2 weight percent of the total weight of the composition, anti-foaming agent in an amount of 0.1 to 0.4 weight percent of the total weight of the composition, bactericide in an amount of 0.1 to 0.3 weight percent of the total weight of the composition, and finely ground calcium carbonate or organic pigment in an amount from 40 to 60 weight percent of the total weight of the composition, the remainder being water, and wherein the at least one binder in dry form can be present in an amount from 0.5 to 3 weight percent and wherein the first alkaline agent is 25% strength ammonia and can be present in an amount from 0.2 to 0.6 weight percent of the total weight of the composition.
According to an embodiment of the present invention, the film-forming opacifying composition is slightly alkaline and comprises at least two binders constituted by two resins based on acrylic derivatives, having an acid index greater than 60, one being in solid form and the other being in aqueous dispersion; and at least one filler or pigment.
This filler can be selected from calcium carbonate, silica, silicate, barium sulphate, titanium oxide, or zinc oxide. The pigment can be selected from mineral or organic colored pigment.
This composition has good rainwater resistance. After being coated and dried, the composition is capable of being removed easily and quickly by spraying a slightly alkaline aqueous solution containing 0.2-3% by total weight, of one or more alkaline agents selected, for example, from sodium hydroxide, sodium carbonate, or sodium salt of ethylene diamine tetraacetic acid (EDTA).
It must be noted that this substance also has the property of being eliminated completely by an acid based solution non-classified as irritant.
This efficiency is obtained due to the presence, in slightly alkaline aqueous medium, of a specific binder in the composition. It is a resin or the combination of a plurality of resins based on acrylic derivatives, having a high acid index (greater than 60), contrary to the aqueous dispersions of styrene acrylic ester copolymers or of acrylate copolymers that are currently used, and which remain nonsaponifiable.
A good compromise between rainwater resistance and ease of subsequent elimination of the opacifying film in slightly alkaline medium can be obtained by associating two acrylic binders having a high acid index (one in solid form and the other in aqueous dispersion).
By varying the proportion of one with respect to the other, one promotes either the ease of elimination (due to the solid acrylic), especially in the case of precocious elimination of the opacifying film, or rainwater resistance (due to the acrylic in aqueous dispersion).